Ignore channels without xmltvid when guessing if the xmltv grabber has done something.

Description

One of my sources gets 28 days of guide data on one channel via EIT and 21 days on other channels via XMLTV. So the grabber has no chance to change max(endtime) of this source and is always reported as "potentially failed".

Attached is a proof of concept patch that ignores channels without xmltvid (the grabber can't change them anyway)

Only consider channels which have an xmltvid when checking whether
mythfilldatabase inserted any data. This will better handle error
reporting for users who have sources with different channels using XMLTV
(or Schedules Direct) and EIT.